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Small Word Clock 



.1 



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Small Word Clock 



Written By: Robert Gill 



-/ TOOLS: 

Epoxy, quick-setting (1) 

Hot Glue gun & hot glue (1) 

Rotary tool with cut-off wheel (1) 

Sand paper (1) 

Soldering iron (1) 

UV light box (1) 

Wire cutters (1) 

Wire stripper/crimper (1) 



PARTS: 

arduino nano 3.0 (1) 

DS3231 RTC(1) 

MAX7219 LED Controller (2) 

5mm momentary button/switch (4) 

resistors (value depends on LEDs used) 
121 

4.7k Resistors (pull-down resistors) (4) 

.1 uf Ceramic Capacitor (2) 



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10 uf Electrolytic Capacitor (2) 
White 1210 SMD LED (114) 
DIP socket for Arduino Nano (1) 
Double-sided photoresist PCB 6in x 6in 

tu 

Photoresist PCB 4in x 6in (1) 
6 1/8 in x 6 1/8 in clear acrylic sheet (1) 
Frame for the clock (1) 
Stiff cardboard (not corrugated) (1) 
Tracing paper (for light diffusion) (1) 
Power Supply. 5V DC. regulated 1A 
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Small Word Clock 

minimum (1) 
Rare earth magnets (8) 
Hookup wire, solid core (1) 
• Solder Flux (1) 

CR2032 coin cell battery (1) 
CR2032 coin cell battery holder (1) 
10mm vinyl bumpers (4) 
DC barrel jack (1) 



SUMMARY 

This word clock has a lot of small steps that add up to a moderately difficult build. You'll be 
building three circuit boards, possibly making (or modifying) a frame, soldering SMD parts 
and playing around with finicky die-cut stickers. 

However, the end result can be very satisfying. If you're concerned about doing some of 
these steps yourself, there are many on-line services that you can use to make your life 
simpler. The circuit board files can be sent away, the light guide can be laser-cut, and you 
can probably custom-order a frame to your dimensions from the local art store. 



Step 1 — Planning 

• The frame for this project can be anything that you can find, but make sure it is at least an 
inch deep. This will give you space for the light guide, circuit boards and wire. 

• The frame needs to have an internal dimension of 6 inches x 6 inches. For my frame, that 
meant the outside dimension was about 6 1/4 inches square as the aluminium was 1/8 in 
thick. 

• The acrylic front piece needs to be cut to the same dimension as your frame. Likewise for 
the vinyl sticker and the back board. 

• The back board can be almost any material but it should be a little firm as it will hold 4 
buttons and you don't want it buckling under pressure. 

• Download the Arduino code. Fritzing and Illustrator files from github . 



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Small Word Clock 



Step 2 — Prepare the circuit boards 




• You need to create three different circuit boards - one for the Arduinio, one for the buttons 
and one for the lights. The PDF and Fritzing files for each circuit board are linked above. 
The PCB for the lights is the most challenging as it is largish, quite detailed and double- 
sided. 

• I won't describe the full steps for creating the circuit board as there are many excellent 
tutorials already on the web. I used Colin Cunningham's YouTube video for my inspiration . 

• The biggest challenge for the double-sided PCB is lining up the two sides of the board prior 
to exposure. After printing out the templates on transparencies, place double-sided foam 
tape around three sides (using your PCB as a guide for size). Remove the PCB and line up 
the two sides. Holding the transparency in place, lift one side of the top transparency, 
remove the protective strip from the tape and press the transparency in place. Repeat for 
each corner and you will have a pocket for the circuit board that will keep everything snug 
when it is being exposed. 

• Be sure to use two layers of each "negative" - I found the UV light was strong 
enough that my circuit board was washed out with only one layer. 



A 



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Small Word Clock 



Step 3 — Drill the circuit boards 




• Each circuit has several holes to drill, none more so than the light PCB. I used an 0.8mm 
titanium drill bit as regular bits will not stay sharp drilling into the fibreglass material the 
PCB is made from. 

• I was concerned that not having a drill press would lead to poor-quality holes, but the PCB 
is so thin that it was not a problem to "freehand" the drilling. 



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Small Word Clock 



Step 4 — Soldering - Part 1 




• Starting with the Arduinio board, solder in the header pins, DIP socket and power supply 
barrel jack. Next, solder the tactile buttons, pull-down resistors and if you like, the hook-up 
wire. 

• There are many through-hole vias on the LED PCB. I used leftover wire from snipping off 
the leads of components from prior projects. 

• Begin by placing the wire in place and soldering on one side. 

• Then flip the board over and solder the other side. Now you can snip the excess wire from 
each side. 

• Do only one row at a time on each side before flipping it over as it is easy to lose track of 
what has been soldered and what is still remaining. 

• Remember that not all the holes require a through-hole via. There are a few header pins, a 
coin-cell battery holder and some other resistors. 



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Small Word Clock 



Step 5 — Soldering - Part 2 




• Soldering the SMD LEDs on to the main PCB was the most intimidating part (at least for 
me). However, once I got going things went quite smoothly. 

• Begin by soldering the MAX7219 LED controllers, remembering that many of the pins 
require contact on both sides (so soldering on both sides of the board is necessary). 

• To solder the SMD LEDs, apply a very small piece of solder to the pad for the LED. Then, 
apply some flux to the solder you have just applied to the board. Next, with one hand, use 
some pliers to put the LED in place and then touch the soldering iron to the pad very 
briefly. Repeat 113 more times. 

• Solder the capacitors (the big one has polarity - so double-check that it goes in the right 
way), resistors and header pins. 

• The value of the resistor is very important - see this page for information on how 
to calculate the value appropriate for the LEDs you are using . 



A 



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Small Word Clock 



Step 6 — Soldering - Part 3 







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• Soldering the DS3231 is also a little 
tricky - see this YouTube clip for 
tips on how to solder SMD pieces - 
but with a bit of patience it's not so 
bad. Use a similar method to that 
used for the LEDs. 

• Place a drop of solder on the 
board 

• Apply flux to the solder 

• Hold the part in place using 
small pliers while you solder it in 
place. 

• Solder any last pieces, including 
the coin-cell battery holder 



Step 7 — Send the code for the Arduino to the device. 



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• There are many tutorials for 
completing this step and the 
Arduino website is a great 
resource. 



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Small Word Clock 



Step 8 — Test the circuits 




• Connect the circuits and test the device. I found I had a few bad solder connections, and a 
few scratches had broken my traces so I had to apply some solder to repair those points. 

• You may also find an LED is not working correctly - check the connections first, and then 
try replacing the LED. I had at least one that was defective. 



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Small Word Clock 



Step 9 — Light guides 




• Using a utility knife, cut strips of cardboard about 1cm wide and at least 6 V2 inches long. 
You will need about 20 of these. 

• Next, place a guide on the east-west axis and mark off the spaces between the LEDs. 
Repeat for the north-south axis. 

• Place 10 pieces together and using a rotary cutter, cut notches half-way down at the points 
you marked off. Make the notches as wide as the cardboard. 

• Fit together the pieces of cardboard into a grid. Remember that it is a not a square grid and 
that the east-west and north-south spacings will be different 

• Cut the grid to the size of your circuit board and if necessary, sand off the edges so that 
the edge of the light guide is flush with the edge of your frame. 



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Small Word Clock 



Step 10 — Prepare the letter stencil 




• I went to a local commercial printer to get the vinyl sticker die-cut. The Illustrator file is 
attached above. The sticky side needs to be on the "right" side. When the sticker is 
applied to the acrylic backing you want to be able to look through the acrylic and be able to 
read the text normally. 

• When it comes from the printer, you will have to remove the letters. This is pretty finicky 
so take your time, use a utility knife to lift the letters out and pliers to hold the internal 
spaces in place (the gap in the "R", "A", and "O" is especially tricky). 

• After all the letters have been removed, place the backing material (supplied by the printer) 
on to the letters. This will hold everything in place when it is placed on the acrylic 



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Small Word Clock 



Step 11 — Apply the letter stencil 




• Remove the protective paper from the acrylic and lay the piece down on a clean work 
surface. 

• Remove the backing from your stencil and carefully line up the edge of your stencil to the 
edge of the acrylic. 

• The backing will be slightly sticky - use this to your advantage by pressing it into your 
work bench. It will keep everything in place while you proceed. 

• Working very slowly, use a credit card to incrementally apply the stencil to the acrylic. 
Take your time and work the credit card back and forth to get the smoothest possible 
finish. 

• Remove the backing from the stencil and check for any major bubbles. I've found that 
some of the small bubbles will disappear with a bit of vigorous rubbing. 



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Small Word Clock 



Step 12 — Prepare the frame 




• Assemble your frame and paint to your desired finish. The frame I used was originally 
unfinished so I primed the bare metal before spray-painting a flat black finish. 

• The Arduino PCB has the power supply so it needs to be mounted somewhere sturdy for 
when the barrel is inserted. I used the edge of the frame and epoxy resin to affix nuts 
through which the board could be attached. 

• You might also need to put down a layer of hot glue on the frame to act as an insulator 
between the bottom of the Arduino PCB and the frame - you could get some short circuits 
if the two come in contact. 



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Small Word Clock 



Step 13 — Cut the back board 




• Using a utility knife, cut the back board to the size of your frame. Line up the power supply 
and cut the hole for the power supply. You can use a drill to mark the corners which will 
make things go a little smoother 

• For the buttons, mark and cut four square holes. It is mostly a matter of aesthetics as to 
where the buttons go, but be sure to check that the frame is clear of the PCB. 

The button PCB might have some raised solder points. To make sure that the buttons are 
flush, you can scrape away some of the board. 

The back board needs to be securely fastened to the frame. As the corners of my frame 
were steel, I was able to use a rare-earth magnet in each corner. I used hot glue to attach 
a small piece of metal to the board and quickly held it in place while the glue set. 



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Small Word Clock 



Step 14 — Attach the acrylic front sheet to the frame 




This step will vary somewhat 
based on the type of frame you 
have used. If you have used a 
regular picture frame you can 
probably skip this step altogether. I 
used rare-earth magnets to hold 
the front sheet to the frame. 

Create a block of cardboard (I used 
leftovers from the light guide) to the 
appropriate height, leaving enough 
room for a magnet and a small 
piece of metal. The metal has to be 
large enough for a strong magnetic 
pull, but it also has to keep clear of 
the lettering. Since the front sheet 
is not that heavy you can probably 
get away with a piece about the 
same size as the magnet. 

Glue the magnet to the cardboard 
block with hot glue. Next, place 
your piece of steel on the magnet. 
Place a dab of hot glue on the steel 
and quickly press your front sheet 
to the frame. After a few moments 
you can pull the front sheet away 
and the steel piece should now be 
in place. 



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Small Word Clock 



Step 15 — Putting it all together 




• Begin by hooking up all your electrical connections (see the attached document for 
guidance) and insert the coin-cell battery in the holder. 

• Next, place the light guide/grid on the LED circuit board and slide everything into the 
frame. 

• Next screw down the Arduino PCB firmly in place. 

• You will probably need some sort of spacer to keep the LED PCB tight to the front of the 
frame. Cut a few small squares of foam-core board of cardboard just a bit larger than your 
gap. Slide these wedges into the space between the frame and the PCB and it should fit 
snugly. 

• The buttons can be hot-glued in place, using a piece of cardboard or foam-core board to 
build it up to the appropriate height. 

• Attach small plastic bumpers to the bottom of the frame to give it a sturdy base, snap on 
the front and back panels and the job is almost complete. 



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Small Word Clock 



Step 16 — Light diffusion 




• You need to place a film of some 
sort between the LEDs and the 
acrylic front sheet. This will ensure 
that the letters light up from all 
angles in a smooth and even way. 

• I experimented with a few things 
but found a piece of cheap tracing 
paper works well. Cut a square of 
material a touch smaller than your 
front piece. No need to glue it in 
place as the magnets will do the 
job for you. 



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Small Word Clock 



Step 17 — Clock operation 




• As soon as you plug in the power supply the clock will light up. You may see some lights 
flashing at first, but this is normal. 

• The clock has four buttons. Button 1 sets the hour, button 2 sets the minutes, button 3 
cycles through the clock modes and button 4 changes the brightness. 

• The three clock modes are: 

• The default mode displays the time with each dot in the corner representing a minute 
increment. In the picture to the left, the time is 10:27. 

• The next mode displays the time with the corner dots advancing on each second 

• The next mode displays the seconds. 



This Flickr post was my inspiration and was also the basis for the Arduino code used in this 
project. 



This document was last generated on 2012-10-30 11:35:25 PM. 



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Page 17 of 17